Added fix to the partitioning

The choose_part_count function that is important for creating an irregular mesh partitioning wasn't behaving as expected. Due to operator precedence the values of R and Q weren't being decremented, instead the operation was being applied to the pointer itself and hence odd things were happening. Fixed with some simple bracketing.

macsio/macsio_data.c

@@ -35,7 +35,6 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #include <string.h>
 #include <time.h>
 
-
 /*!
 \brief Support functions for Perlin noise
 @{
@@ -1024,6 +1023,7 @@ make_mesh_chunk(int chunkId, int ndims, int const *dims, double const *bounds, c
 }
 
 static int latest_rand_num = 0;
+static int run_seed = 0;
 
 static int choose_part_count(int K, int mod, int *R, int *Q)
 {
@@ -1035,24 +1035,24 @@ static int choose_part_count(int K, int mod, int *R, int *Q)
     {
         if (*R > 0)
         {
-            *R--;
+            (*R)--;
         }
         else if (*Q > 0)
         {
             retval = K+1;
-            *Q--;
+            (*Q)--;
         }
     }
     else
     {
         if (*Q > 0)
         {
-            *Q--;
+            (*Q)--;
         }
         else if (*R > 0)
         {
             retval = K;
-            *R--;
+            (*R)--;
         }
     }
     return retval;
@@ -1156,7 +1156,15 @@ MACSIO_DATA_GenerateTimeZeroDumpObject(json_object *main_obj, int *rank_owning_c
     rank = 0;
     chunk = 0;
 
-    srand(0xDeadBeef); /* initialize for choose_part_count */
+    /* If we haven't set a seed for the run then take this from the clock.
+     * This should allow us to randomise the decomposition between runs but
+     * still use this overloaded function to identify chunk ownership within
+     * a single run
+     */
+    if (run_seed == 0){
+        run_seed = time(NULL);
+    }
+    srand(run_seed); /* initialize for choose_part_count */
     latest_rand_num = rand();
     parts_on_this_rank = choose_part_count(K,mod,&R,&Q);
     for (ipart = 0; ipart < nx_parts; ipart++)